Improvement in molding earthen covers



W. S. THOMPSON.

Improvement in Molding Earthen-Covers.

No. 128,437, PatentedJune'25,187 2.

W M11 71 m waa mt interior depth of the cover.

PATENT OFFICE.

WILLIAM S. THOMPSON, OF ROCHESTER, NEW YORK.

IMPROVEMENT IN MOLDING EARTHEN COVERS.

Specification forming part of Letters Patent No. 128,437, dated June 25, 1872.

Specification describing a certain Improvement in Covers for Fruit and other Jars, invented by WILLIAM S. THOMPSON, of the city of Rochester, in the county of Monroe and State of New York.

My invention consists of the process of forming earthen covers for jars, viz., by a single screw which strikes into a mold and performs the double function of pressing the cover and cutting the screw-thread at one and the same operation, as will hereinafter be more fully described.

In the drawing, Figure 1 is a vertical section of my improved cover; Fig. 2, a diagram, showing the method of forming the cover.

A represents the cover, which is made of clay or equivalent plastic material, with an -internal screw-thread, a, adapted to fit directly the male screw upon the neck of the jar without the intervention of other parts. After being properly formed, as above described, the covers are baked in the usual way of treating earthenware, which gives solidity and strength.

To form this cover I employ this process: A body of clay or equivalent plastic material is filled into a mold of the exterior form of the cover, as shown in Fig, 2. a screw of the same size as the internal diameter of the cover, and threaded upon .the outside to correspond with the threads to be produced upon the interior of the cover. This screw is turned down a distance equal to the The action producedis a double one: first, the cavity is pressed or formed, which gives the cover shape in the mold; and second, the internal threads of the cover are formed by the corresponding ones on the screw. The screw is then turned back and the molded cover removed and baked or otherwise properly prepared, as before described.

The advantages of this cover are as follows; It is adapted to fit direct, and to screw upon the top of afruit or other jar without the intervention of other parts. Heretofore a cover fitting thejar direct has had to be made of sheet metal,

Above this mold is I such as zinc or tin, swaged or spun up in proper form. Such material is objectionable, since it corrodes and taints the fruit and soon leaks air. It has been difficult to form a glass cover with internal threads, since, in the ordinary modes of pressing glass, the molds cannot be made to work,-and the screw-threads cannot be cut with the glass cold, owing to its hardness. Another difficulty occurs with the use of glass, which forms air globules, and therefore gives passage to the air inward. Hence, in order to use glass over the fruit, a glass disk has to be first made, and then a metallic screw rim or clasp, which passes over the threads of the jar and presses the glass disk down. This involves large extra cost, and is more difficult in use. In my case the simple molded cover answers the purpose, no outside attachment being necessary. It is cheaper than either the single metallic cover or the combined metal and glass. It is indestructible, never corrodes or taints the fruits, and presents a handsome appearance, as it contrasts with the glass. I design to enamel or glaze it, not only to give a better finish, but to prevent passage of air through the pores; but I do not confine myself to such, as it may be treated with-oil or in any other way to close the pores; and in the use of some plastic material no such treatment may be necessary.

I do not claim a glass cover with an internal thread; but

What I claim, and desire to secure by Letters Patent, is

The process of forming earthen covers, viz., by a single screw which strikes into a mold and performs the double function of pressing the cover and cutting the screw-thread at one and the same operation, as set forth.

In witness whereof I have hereunto signed my name in the presence of two subscribing witnesses.

W. S. THOMPSON. Witnesses:

' R. F. Oseoon,

ARcHm BAINE. 

